1. Field of the Invention
The present invention relates to automatic machining devices and, in particular, machining devices of the type wherein successive machining operations are performed on a workpiece at different machining stations.
2. Prior Art
For machining workpieces that require a large number of repetitive machining operations, it is desirable to automate as many of the machining operations as possible. By automating all or a large percentage of the machining operations, it is often possible to reduce the labor costs involved in machining the workpiece and at the same time eliminate a monotonous and unchallenging manual task.
One form of apparatus for performing a number of machining operations comprises a rotatable table having a plurality of workpiece holding members and a plurality of machining stations spaced about the periphery of the table. A workpiece is loaded onto a workpiece holding member and the rotatable table is indexed so that the workpiece passes before successive machining stations so the machining tool associated with each machining station may perform a machining operation upon the workpiece. After the workpiece has been indexed through the entire succession of machining stations, it may be unloaded at the original loading station or an unloading station which may be adjacent the loading station.
An example of such an apparatus is disclosed in U.S. Pat. No. 3,720,475. A centrally located indexing table, having a generally circular shape when viewed from above, supports six chucks for holding workpieces. Four machining devices are arranged about the worktable and, together with loading and unloading devices, constitute six work stations. The six work stations are spaced about the indexing table such that the indexing table may be positioned to place each chuck adjacent a work station so the device at each station may perform its operation on a workpiece held in an adjacent chuck simultaneously with the other devices at the other work stations.
Certain of the work stations include vertically oriented drilling machines mounted on reciprocating slides. The slides are reciprocated by the interaction of a cam mounted on the slide and an eccentric cam mounted on a fixed shaft which is rotated by a motor. Another station includes a horizontally disposed drilling device which is supported on slides such that it can be displaced toward or away from the indexing table and a workpiece supported by it.
A disadvantage of the above described apparatus is that each work station is capable of performing only one machining operation upon a workpiece before it. Such a table has severe limitations with respect to the total number of machining operations that can be performed and would be unsuitable for performing a large number of repetitive machining operations upon a workpiece. In addition, there is no disclosure regarding motor structure within the indexing table which would actuate the indexing table and accurately locate the chucks before each work station. Such indexing and locating structure is essential for machining operations requiring high tolerances. Furthermore, the construction of the indexing table and the arrangement of the vertically oriented drill prevent the device from being adapted to perform machining operations on large, plate-like objects which may be too large to be placed upon the indexing table in a horizontal plane.
Another example of a device for performing repetitive operations on a plurality of workpieces is disclosed in U.S. Pat. No. 581,830. This device is designed to manufacture buttons and comprises a rotatable turret which supports a plurality of chucks evenly spaced about the periphery of the turret. A plurality of drills are mounted on fixed platforms about the turret and are spaced so that the chucks may be placed in registry with the drills by rotation of the turret. At each of the drilling stations there is a single drill which is capable of performing a single drilling step at a single location.
The apparatus disclosed in this patent possesses the same shortcomings as the apparatus previously discussed. Since each work station contains a machining tool capable of performing only one machining operation at one location, the entire apparatus is severly limited in the number of machining operations it is capable of performing. While the device does possess a pawl arrangement for locating the turret as it is rotated from station to station, such means is not sufficiently accurate to provide precision location of the workpiece holding members with respect to the work stations to allow close tolerance machining operations. Furthermore, the workpiece holding members cannot accommodate large, plate-like workpieces which require substantial vertical space both above and below the indexing table.
Accordingly, there is a need for an automatic machining device which has the capability of performing multiple machining operations at each work station, thus greatly increasing the total number of machining operations that can be performed by a single device, without a concomitant increase in the size of the indexing table or the number of work stations. In addition, there is a need for an automatic machining machine having an indexing table which is capable of supporting large plate-like workpieces which require substantial space both above and below the surface of the indexing table. Furthermore, there is a need for indexing tables forming part of machining devices which include locating apparatus which permits accurate location of workpiece holding members before each machining station to allow machining operations to be performed having sufficiently close tolerances.